1. Field of the Invention
The present invention relates to an electric power steering apparatus.
2. Description of the Related Art
An electric power steering apparatus is structured, as described in Japanese Patent Application Laid-Open No. 2001-315652 (patent document 1), such that a yoke of an electric motor is fixed to a housing, an assist shaft of a steering apparatus is supported to the housing, and the assist shaft is connected to a rotation shaft of the electric motor. A rotation force of the electric motor is transmitted to the steering apparatus, thereby assisting steering force applied to the steering shaft by a driver of a vehicle.
In the conventional electric power steering apparatus, a brush holder of the electric motor is clamped between the yoke of the electric motor and the housing, and a communication passage allowing ventilation between an inner portion of the yoke in the electric motor and an inner portion of the housing is provided in a partition wall. Therefore, when the temperature of an internal space of the yoke in the electric motor changes in correspondence to heating or cooling of the electric motor as a result of operation of the electric power steering apparatus, the internal air is transmitted between the inner space of the yoke and the inner portion of the housing. This prevents an ambient air containing moisture from intruding into the inner portion of the yoke so as to generate a dew condensation where internal air of the yoke in the electric motor is transmitted between the inner space of the yoke and the external portion of the apparatus.
The prior art has the following problems.
(1) There is a risk that grease applied to a periphery of the assist shaft in the inner portion of the housing is scattered at a time of operating the electric power steering apparatus in which the electric motor is assembled in the housing. Such scattered grease intrudes into the inner portion of the yoke of the electric motor from the communication passage provided in the partition wall, thereby causing a malfunction of the electric motor.
(2) There is a risk that in a preliminary stage before assembling the electric motor in the housing, dust in the ambient air intrudes into the inner portion of the yoke of the electric motor from the communication passage provided in the partition wall, thereby causing a malfunction of the electric motor.
An object of the present invention is to prevent foreign materials from making an intrusion into an inner portion of the electric motor, in an electric power steering apparatus in which a communication passage allowing ventilation between an inner portion of a yoke of the electric motor and an inner portion of a housing is provided in a partition wall of a brush holder.
The present invention relates to an electric power steering apparatus comprising a yoke of an electric motor fixed to a housing, an assist shaft of a steering apparatus supported to the housing, where the assist shaft is connected to a rotation shaft of the electric motor. A brush holder of the electric motor is clamped between the yoke of the electric motor and the housing. A communication passage is present allowing an inner portion of the yoke in the electric motor and an inner portion of the housing to be ventilated, the communication passage being provided in a partition wall of the brush holder.
Shielding means opposing each other are disposed in an opening facing the inner portion in a side of the yoke in the communication passage arranged in the brush holder, via a narrow passage.